1. Field of the Invention
This invention relates to a circuit for use in a factory automation apparatus, for example, a numerical control apparatus, a programmable controller, a robot controller and the like.
More specifically, this invention relates to an input module of the factory automation apparatus, which is used to input binary information into the apparatus.
2. Description of the Related Art
Signals from push button switches, limit switches, and the like are ON/OFF signals and may be called "binary information." This binary information can be used in numerical control apparatus, programmable controllers and robot controllers, and the like, in order to input these ON/OFF binary information to perform various kinds of control. Input circuits of these apparatus are constructed on a single printed circuit board or in a module circuit like a large scale integration circuit and are called input modules.
In the related art, there have been three kinds of input modules because of the different power sources used for generating the binary signals.
These are "input module for DC with plus common", "input module for DC with minus common", and "input module for AC".
The related art of input modules are shown in FIG. 11 and FIG. 12.
FIG. 11 shows an example of an input module circuit used in a circuit which uses DC 24V as the power source of an input signal. The voltage of power source 100 is switched ON/OFF by switch 102 and divided by the divider circuit that includes resistor 103 and resistor 104.
The divided voltage becomes a suitable voltage for a binary signal and is applied to light emitting diode 105a of photo coupler 105. When the light emitted by the ON/OFF signal of light emitting diode 105a reaches the photo transistor 105b in photo coupler 105, it causes photo transistor 105 to turn ON/OFF. Then the binary information of photo transistor 105b is sent to an internal circuit of an associated apparatus, for instance, to the programmable controller. The circuit of FIG. 11 is an example of a minus common type circuit in which the minus pole of power source 101 is a common line. If the polarity of photo diode 105a in photo coupler 105 is reversed, power source 101' having a common line of the plus pole is applicable.
The other example of an input module is shown in FIG. 12, in which an AC 100V power source is used. This example is different from FIG. 11 in that there is a dividing circuit using an impedance of capacitor 107, and bidirectional photo coupler 108 is used instead of unidirectional photo coupler 105. Since the rest of this circuit is identical to and operates in the same manner as in the circuit in FIG. 11, a detailed description is believed unnecessary. As described above, the related art input module includes an AC power source, a voltage dividing circuit and a bidirectional photo coupler for an AC input signal, and also includes a DC power source and an unidirectional or bidirectional power source for a DC input signal.
Therefore, in the related art, the electrical parts are different depending on kind of the power source which is used in the control apparatus. Thus, it is requested that special type of input modules are prepared in response to the power source which is used.
Thus, manufacturers of input modules must make and prepare various kinds of input modules for different demands of users. This results in complexity in the production line, complexity in the process control, and a problem of a large amount of storage space.
Further, OEM manufacturers must use input modules properly, test them, and confirm various kinds of input modules. This also results in complexity of manufacturing and quality control.
Furthermore, end users must also keep many kinds of input modules. This is also inconvenient.
Accordingly, it has been desirable to provide an input module which is able to deal with various kinds of power sources by preparing only one kind of input module.